(a) Field of the Invention
The present invention relates to a thinner composition for removing spin-on-glass and photoresist which is used in the semiconductor component manufacturing process. More particularly, the present invention relates to a thinner composition that can be used in washing and removing the unnecessary spin-on-glass ("SOG") of an SOG layer at edges and a backside of a substrate, the SOG layer being produced when an oligomer solution of an organic silicon compound having a siloxane bond is spin-coated on a substrate during the formation of an intermediate insulated layer. The present also relates to a thinner composition that can be used in washing and removing photoresist from the edges and the backside of a substrate, the photoresist being used as a mask in a photolithography process.
(b) Description of the Related Art
The width and distance of components, i.e., the distances between the dimensions of metal wiring are experiencing increasing reductions as Large Scale Integrated circuits ("LSI") become microscopic, highly integrated, and multi-layered. On the other hand, the component height of metal wiring, etc. has withnessed only minimal reductions so as not to increase wiring resistance and electric current density. Therefore, as side gap dimensions between metal wirings are becoming extremely narrowed, wiring height must naturally increase. As this type of wiring is formed by high anisotropic etching, the edges of the wiring have a sharp slope, and the number of wiring crossings and holes increase. Furthermore, the surface topography of LSI chips becomes greater due to the multi-layering of the wiring.
When wiring is formed on a surface with such severe protrusions and depressions, anisotropic wiring etching can leave residue at the sides of walls where there is a substrate topography that can lead to short circuits. In order to resolve this type of problem, there is a need to planarize sublayers to a minimum between wiring layers. Particularly, when the surface of an intermediate insulated layer on the primary aluminum wiring layer has not been sufficiently planarized, this leads to wiring short circuits on the upper layer and faults in confidence testing.
Accordingly, a siloxane oligomer solution, referred to as spin-on-glass (SOG), is used for the purpose of both acting as an intermediate insulated layer between wiring in the semiconductor multi-layer wiring process and planarizing a wiring layer before the next wiring process. Such SOG is typically structures such that an alkyl group side chain is bonded to a main chain of --Si--O--Si-- as represented in the below General Formula 1: ##STR1##
where n is an inter equal to or greater than one.
The above SOG has been disclosed in literature (Journal of Vacuum Science and Technology Vol. A9 No. 5, 1991, p2696), patents (Japanese Laid-open Patent No. Showa 62-230828, Japanese Laid-open Patent No. Heisei 7-40 242747, and Japanese Laid-open Patent No. Heisei 9-260384), and other publications.
Furthermore, a material which provides the SOG with a photosensitive characteristic on an insulated layer capable of patterning in a semiconductor device was disclosed in Patents including Japanese Laid-open Patent No. Heisei 9-36110, and Japanese Laid-open Patent No. Heisei 8-203876.
In the formation of an intermediate insulated layer, when the oligomer solution of an organic silicon compound having a siloxane bond is spin-coated on the substrate and baked, the insulated layer of silicon oxide material is made by heated condensation polymerization. In this spin-on-glass process, a solution is used to penetrate into the microscopic wiring, filling in level differences to be evened out. A low temperature process is possible as condensation polymerization occurs below 400.degree. C. Furthermore, regular processing technologies such as the conventional etching, etc., can still be employed as the resulting insulated layer is a silicon oxide substrate.
Although the process in which this SOG solution is spin-coated to form a film is similar to the below described photolithography process, the process for washing and removing the undesired SOG coating, generated during spin-coating, at the edges and backside of the substrate is essential.
A thinner composition can remove the SOG coating at the edges and backside of the substrate quickly and thoroughly. It is also useful in removing undesired photoresist generated when a photosensitive resin composition is spin-coated. The photoresist is used as a mask in the photolithography process for the microscopic circuit patterning.
The photolithography process in the semiconductor component manufacturing process is an electronic circuit forming technique accomplished through the steps of coating a photoresist on a substrate, transferring a pattern according to the original design, and cutting according to the transferred pattern, i.e., the etching process.
This photolithography process is performed through various processes including:
a) a coating process in which a photoreist is uniformly coated on a substrate; PA1 b) a soft baking process in which a photoresist is adhered to a wafer surface by evaporating a solvent from of the coated photoresist; PA1 c) an exposing process in which a mask pattern is transferred on the substrate by the consecutive scale-down projection of a light source, such as ultraviolet rays, into a circuit pattern on the mask repeatedly to thereby expose the substrate; PA1 d) a development process in which the areas having different physical properties, such as a difference in solubility due to the photosensitive-activity resulting from exposure to the light source, are removed using a developer; PA1 e) a hard baking process in which a residual photoresist on a substrate is more strongly affixed after the development process; PA1 f) an etching process in which certain parts are etched to provide electrical characteristics according to a pattern of the developed substrate; and PA1 g) a stripping process in which unnecessary photoresist is removed after the above processes.
Multiple microscopic circuits are formed on a substrate in order to ultimately manufacture an integrated semiconductor circuit through this photolithography process. Foreign materials, for example particles, should be eliminated to prevent their introduction into the fine gaps between the circuit wiring in these processes. Particles existing on a substrate can cause the various faults in the subsequent processes, such as etching, ion implantation, etc., resulting in decreased total productivity. It has been found that the main source of these unwanted particles is the unused photosensitive solution present at the periphery of the coated substrate.
In the above photolithography process, these edge beads of photosensitive materials can be produced after the spin-coating process in which a photoresist is applied to a substrate and the substrate is then rotated making the photoresist spread out evenly on the surface by the action of centrifugal force.
Photoresist inclined toward the edge and backside regions of a substrate by the centrifugal force is formed into small spherical shapes in this spin-coating process. This spherical shapes can be a source of particles in the apparatus after it is passed through the baking process and can be released during the transportation of a substrate, or can become a source of defocus during the light exposure process. As these undesired photosensitive materials become a source of apparatus contamination, reducing the yield of the semiconductor component manufacturing process, a spray nozzle is installed at edge parts of the substrate and at the upper and lower backside parts. A thinner composition composed of organic solvent constituents is sprayed through the nozzles to remove these excess photosensitive materials.
The practical aspects of chemically amplified resist are reviewed as follows. In a patterning method using a chemically amplified resist employing a novolak phenolic resin, a problem results in that a pattern which was formed by an absorption effect caused by a binder resin and a cross-linking resin becomes a reverse taper when an exposing light source was changed from the conventional G/I-line light source to an excimer laser light source (Journal Vacuum Science Technology., Vol. B7, p1771, 1989).
A positive type chemically amplified resist was suggested in literature as an alternative for this (Proc. SPIE., Vol. 1262, p32, 1990). This chemically amplified resist has a multi-constituent composition comprising an acid generator which produces acids when it is irradiated, and a compound which is reacted by these acids. A polymer compound which is reacted by these acids is known to have a structure as represented in General Formula 2: ##STR2##
wherein n is an inter greater than or equal to one, and R is an alkoxycarbonyl group, alkyl group, alkoxyalkyl group, alkylsilyl group, tetrahydropyranyl group, alkoxycarbonyl methyl group, etc., compounds which can be easily decomposed when reacted by acids. As it has as a main constituent, a polymer compound such as a polyvinyl phenol derivative in which photoabsorption occurs in the short wavelength range, the chemically amplified resist becomes more transparent, and has a high sensitivity and resolution as a resist reaction progresses by a chain reaction due to an acid catalyst.
A polyvinyl phenol derivative receives a strong multiple reflection effect by light reflected from a lower part of the substrate due to a high transmittance of excimer laser light as described in the above. Multiple reflections within a membrane are generated by interference between the irradiated light (1) and the reflective light from a lower part of the substrate as shown in FIG. 5. FIG. 6 shows that the pattern dimensions vary greatly according to a thickness of the resist film.
Separately, a variety of problems are generated by the type of irradiating source used during the light exposure process. For example, the reflective light interference caused by topography on a semiconductor substrate affects the pattern dimension greatly in case of exposure with a mercury light. When there is a protrusion and a depression or a topography on a substrate, light entering can cause a diffused reflection at an area with different levels generating a halation phenomena, resulting in pattern flow. Consequently, an excellent resist pattern is not formed.
Additionally, as the thickness of the resist layer is different at upper and lower parts of the substrate, the light interference conditions in a resist layer vary causing pattern dimension changes. Furthermore, when exposing with excimer laser light, the ratio of a minute pattern height and width can not be controlled as the proximity effect is generated by the rear dispersion of electrons.
A multilayer resist system using a spin-on-glass coating was suggested (Japanese Laid-open Patent No. Heisei 3-203240) as a method for resolving these problems caused by protrusions and depressions of a substrate surface. A multilayer resist system is a method in which a thick first organic resist layer having high absorbance is coated over the entire surface of the substrate so that protrusions, depressions and topography are planarized. A thin second resist pattern is formed on the first organic resist layer using commonly known photolithography techniques, and this resist pattern is transferred to the above thick first organic resist layer so that an exposed area of the above substrate can be etched. Although the thick first organic resist layer can be directly etched using the above second resist pattern as a mask, it is also good to etch an exposed part of the first organic resist layer using a SOG coating as a mask after a middle layer, such as highly etched resistant spin-on-glass, is formed between both layers, and unnecessary parts of this SOG middle layer are removed. As in the multilayer resist system, protrusions, depressions and topography on the substrate surface were planarized by the first organic resist layer having high absorbance, and a light, which passes from the top through the second resist film formed on the first organic resist layer, is absorbed by the first organic resist layer. Therefore, halation caused by reflection and dispersion of light from the substrate surface, or light interference in the resist film can be reduced, thereby preventing pattern shape dispersion or dimension change.
This method using a multilayer resist system has an advantage in that a high degree of applications are possible with the photolithography as the first resist layer controls the resist pattern characteristics as a mask, and the second resist layer, required for photosensitivity and resolution, can be bonded freely.
For example, this method can be easily applied to extreme ultraviolet photolithography in which an extreme ultraviolet excimer laser light as an excimer light source is employed by using the first resist layer having excellent dry etching resistance and the second photosensitive resist having the high sensitivity and resolution with an extreme ultraviolet excimer laser light with a wavelength of less than 300 nm.
Therefore, the thinner composition can be used in washing and removing undesired coating on the edges and backside of the substrate through such processes as the coating of an SOG solution in order to form an intermediate insulated layer in the semiconductor multi-layer wiring process, to improve layer flatness, in the process of coating the middle layer SOG solution for a multilayer resist system, or in the process of coating each photoresist that is used as a mask in the photolithography.
A dissolution rate and volatility may decide the performance of the above thinner composition.
A thinner composition dissolution rate, as a capability of how effectively and quickly spin-on-glass and photoresist can be dissolved and removed, is crucial.
Particularly, a smoothly treated profile like that shown in FIG. 2 can be made only by a proper dissolution rate in case of an edge area rinsing. When the dissolution rate is too high, a photoresist attack can appear in the rinsing of a photoresist which is coated on a substrate as shown in FIG. 3. When the dissolution rate is too low, a flow phenomena of the partially dissolved photoresist tailings in the rinsing of a coated photoresist on the substrate can occur as shown in FIG. 4. As integrated semiconductor circuits are moving toward higher integration and densities, a low rotation speed is now essential during the rinsing process with larger caliber rotational coaters. However, during the rinse process, whenever the substrate is shaken during a slow speed spin and the proper dissolution rate is not maintained for the sprayed liquid contact speed, then a bounding phenomenon and the increased use of excess fluid can occur. A stronger dissolution rate of thinner is required in the low rpm rinsing process due to the diameter size which is larger than the conventional high rpm rinsing process.
Furthermore, volatility is required so that a thinner is easily evaporated in order that it does not remain on a substrate after the spin-on-glass coating and photoresist are removed. When the volatility is too low such that a thinner can not be evaporated, the remaining thinner itself serves as a contamination source in the each of the later processes, particularly in the subsequent etching process, etc. On the other hand, when the volatility is too high, the substrate is too rapidly cooled so that the variations in film thickness of the spin-coated spin-on-glass and photoresist are increased. Furthermore, easy volatility even during handling can result in contaminating the clean room itself. This in itself causes a variety of faults, such as tailings or photoresist attack, and becomes a direct source for a decrease in semiconductor component manufacturing productivity.
The conventional thinner compositions will now be described.
A method for removing unnecessary photoresist by contact with a thinner in the areas of edge upside parts, edge side parts, and edge backside parts is diclosed in Laid-open Japanese Patent No. Showa 63-69563. For example, the solvents for washing and removing photoresist include ether and ether acetate groups such as cellosolve, cellosolve acetate, propyleneglycol ether, propyleneglycol ether acetate, etc; ketone groups such as acetone, methylethyl ketone, methylisobutylketone, cyclohexanone, etc; and ester groups such as methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, etc. Propyleneglycol monomethylether Acetate (PGMEA) is used as a thinner in Laid-open Japanese Patent No. Heisei 4-49938, and a method using alkylalkoxy propionate as a thinner, etc., is disclosed in Laid-open Japanese Patent No. Heisei 4-42523.
However, although these conventional thinner solvents use a single solvent such as ethylene glycol monoethyl ether acetate (EGMEA), propylene glycol monomethyl ether acetate (PGMEA), and ethyl lactate (EL), there is a problem as it has the following limitations.
That is, although ethylene glycol monoethyl ether acetate is excellent in terms of its dissolution rate, there are problems in that its volatility and flammability are high, and it is particularly toxic and associated with leukopenia and stillborn problems. Propylene glycol monomethyl ether acetate contains .beta. type of materials from its manufacturing processes, and has toxicity problems that may cause birth defects and otherwise be problematic to pregnant mothers. Ethyl lactate can not obtain a sufficient rinsing effect by itself due to its high viscosity and low dissolution rate, and acetone, methylethylketone, etc., have problems of low workability due to their low flash point.
Methods in which the conventional single solvents are mixed were developed in order to resolve these problems the methods and are described below.
A mixed solvent composed of a pyruvic acid alkyl based solvent and methyl ethyl ketone was used as a thinner in Japanese Laid-open Patent No. Heisei 4-130715. A thinner composition composed of a mixture of propylene glycol alkylether and a 3-alkoxypropionic acid alkyl group was used in Japanese Laid-open Patent No. Heisei 7-146562. Additionally, a thinner composed of a mixture of propylene glycol alkylether and butyl acetate, and ethyl lactate, or a mixture of butyl acetate, ethyl lactate, and propylene glycol alkylether acetate was used in Japanese Laid-open Patent No. Heisei 7-128867. A thinner composed of a mixture of propylene glycol alkylether propionate, and methylethyl ketone, or a mixture composed of propylene glycol alkylether propionate, and acetic butyl ester/butyl acetate was used in Japanes Laid-open Patent No. Heisei 7-160008. Also, a mixed solvent composed of propylene glycol alkylether acetate, and propylene glycol alkylether was used as a thinner in U.S. Pat. No. 4,983,490, and a mixture composed of ethyl lactate and methyl ethyl ketone was used as a thinner in U.S. Pat. No. 4,886,728.
However, there have been many problems when the above described mixed solvents are applied to the semiconductor component manufacturing process, especially considering the ever-increasing with high integration and large sized diameters.
For example, a mixed solvent composed of a pyruvic acid alkyl based solvent and methyl ethyl ketone cannot easily dissolve a 1,2-naphthoquinonediazide based photosensitizer (having a high esterification ratio among photosensitizer, and being a main constituent of photoresists). Also using a high volatility solvent such as a mixed solvent composed of propyleneglycol alkyl ether propionate and butyl acetate for rinsing the backside of the substrate cools the substrate and verifies a thickness of photoresist, and using a low volatility solvent such as a mixed solvent composed of ethyl lactate and methyl ethyl ketone reduces the rinsing capability on the substrate edge area. Particularly, solvents such as methyl pyruvate, ethyl pyruvate, etc., are known to corrode metal parts in the used photoresist reservoir fixed to a photoresist spin-coater after prolonged use.
As to the characteristics of the solvents in use, although propylene glycol monomethyl ether is known to have an advantage that increases the photosensitivity of photoresist compared to the conventional ethylene glycol monoethyl ether, i.e., a higher dissolution on photoactive compounds, it can cause discomfort to people due to its bad odor and somatological concerns. Although there was an attempt to mix this with propylene glycol monomethyl ether acetate as a method to mitigate these problems (U.S. Pat. No. 4,983,490), the problems nevertheless remain.